Conductive pillars may be formed on a semiconductor substrate in order to provide a physical and electrical connection for external connectors. These conductive pillars are generally formed through a top passivation layer of the semiconductor substrate, thereby providing an external connection to the active devices formed on the semiconductor substrate. The conductive pillars are formed through typical photolithographic and masking processes, and provide a surface for a conductive bump to be connected.
The conductive bump may be formed on the conductive pillars from a connecting material such as solder. Typically, the connective material may be placed onto the conductive pillars and then heated such that the connective material may partially liquefy and reflow into a bump shape due to the surface tension of the liquefied connective material. Once formed, the conductive bump may then be placed into contact with a separate substrate such as, for example, a printed circuit board or else another semiconductor substrate. After the conductive bump has been placed in contact, the conductive bump may again be reflowed in order to bond the conductive bump to the separate substrate, thereby providing not only an electrical connection between the semiconductor substrate and the separate substrate, but also providing a bonding mechanism between the semiconductor substrate and the separate substrate.
However, the reflow process generally proceeds with the conductive material being on top of the conductive pillar. As such, once the conductive material begins to liquefy, the force of gravity can interfere with the surface tension. This interference can result in a distortion of the bump as the force of gravity pulls the conductive material downwards against the conductive pillar, thereby distorting the overall bump shape.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.